The problem of gas bubbles in a fluid-carrying line is very a long-standing and well-known one. This problem is of considerable importance in various applications in which a liquid is conducted through a conduit, and is particularly troublesome in medical applications. Currently, there is no adequate solution to this problem. Gasses may enter the fluid-filled line in a gaseous state as bubbles within the fluid, or it may be present in a dissolved state within the fluid, and come out of solution under the influence of changing pressures or temperatures. The gas molecules so produced coaless under entropic and hydrophobic influences to form discrete bubbles within the fluid. These bubbles can interrupt and/or block the flow of a fluid. Such blockage or interruption can be problematic for many sorts of medical and industrial equipment where an uninterrupted flow is desirable. Many analytical and diagnostic devices, especially those that employ the flow of very small volumes of a liquid, are very sensitive to such interruptions in flow. When small volumes are involved or at low Reynolds numbers where viscous forces are dominant, the effects of surface tension and other forces at a liquid-gas phase boundary become pronounced and can inhibit flow. These problems are particularly acute in microfluidic applications.
In a medical context, when intubation is required, for example with a catheter, drip or other conduit designed to introduce (or remove) liquid from the body of a subject, such blockage or interruption can have adverse consequences and can even be fatal, such as when an air bubble enters the blood stream. Air embolism (for example venous, pulmonary or cerebral) is a well-known and potentially fatal complication that can occur in patients with central venous catheters (CVCs) as a consequence of the entry of air into the vasculature upon removal of the catheter, and many articles exist describing various methods used to prevent formation of an embolus. Less risk is associated with the use of peripherally inserted central catheters (PICC), but the risk of embolization is still a serious one. Venous air embolism (VAE) occurs mostly during surgical procedures in which the operative site is 5 cm or higher above the right atrium or gas is forced under pressure into a body cavity and is often cited as a complication of neurosurgery, but it can also occur during procedures involving the head and neck, laparoscopic procedures, vaginal delivery and caesarean section, and spinal instrumentation procedures.
The current approach to this problem is to manually prime the fluid line, by flushing fluid through it, just prior to use to ensure removal of any air bubbles present. The operator such as the doctor, nurse or paramedic, visually checks the visually translucent line to determine of any bubbles are present, often tapping the line to dislodge bubbles, and then flushes the line with excess fluid to make sure that any bubbles present are flushed out and that no bubbles are visually present.
Commercial valves and air vents may be placed within the line to prevent gas build-up and so that bubbles that do form may be removed from the line. Valves are usually manually employed by raising the line at the site of the valve so that the bubbles rise to the valve and then opening the valve to flush out any bubbles present.
Commercially available gas/air venting devices are available, particularly for use with medical applications, which are able to vent gas/air from liquid lines without need for manual vents or valves. Examples include IV air filter devices, such as those supplied by Pall Corp and Qosina Corp, and cardiopulmonary bypass surgery blood air filters, such as the Dynamic Bubble Trap by DeWitt Group Int'l and EC Blood Filter® by Pall Corp. These devices use hydrophobic micro-porous membranes to vent gas captured within IV tubes. To allow for sufficient exposure of air pockets/particles with the microporous membranes, the filter divides entering flow into micro-channels. By decelerating the advection rate of the air pockets and increasing the surface area-to-volume ratio, these microchannels allow for air bubbles to have greater contact with the membranes for filtration to occur. However the use of use of these air venting filters is limited primarily by their split channel design, which does not allow for compatibility with catheters, sheaths and endovascular interventional devices that largely require simultaneous passage of liquid and catheters/wires. Other limitations of these current technologies include an inherent dependence on infusion rate (flow rate) to control filtration efficacy, i.e. at higher flow rates, gases pass through the micro-channels faster and carry less contact with hydrophobic vent membranes. Also, the current technologies suffer from undesirable mechanical resistance to flow due to the split channel design. The design of the current invention addresses these three limitations by offering full compatibility with guidewires, catheters and other endovascular devices concurrent with liquid infusion. Since the device separates air/gas from infusing liquid solution, air filtration efficacy is decoupled from infusion rate. In addition, the single, continuous lumen imposes minimal mechanical resistance on flow and infusion capacity.
The current solutions, for example manual flushing of lines of openable valves positioned within a line, present other inherent problems. One current deficit is that the process of recognizing the presence or gas bubbles in the line is visual and requires active checking. Another deficit is that the process of removal of gas bubbles is manual and subject to human error. A further deficit is that such methods cannot remove air bubbles that may arise subsequent to checking and insertion of the line, such as when gas comes out of solution due to the effects of increasing temperature and or decreasing pressure. Another deficit of the current solution is that the efficiency of removal of air bubbles is at least partially dependent upon having a reasonably low fluid flow rate through the line. The faster the fluid flows in the line, the more likely it is that any bubble trapped in the line will pass by any valve and will not therefore be removed. Many infusing solutions (such as radio-opaque contrast solutions) are infused at a relatively fast rate, and thus, the current air venting mechanisms are not a viable solution. None of the current solutions contains an air bubble capture system or bubble trap that removes gas bubbles from the flowing liquid irrespective of the rate of liquid flow through the tube. Additionally, the current solutions do not adequately address the removal of air bubbles arising from the connection or re-connection of fluid lines and insertion of catheters/wires into, for example, a guide/introducer sheath.
There is a long-felt need for air venting devices that trap gas bubbles, that remove gasses from a line irrespective of the rate of fluid flow and that function while allowing insertion of wires, tubes and other solid devices during liquid flow.
Additionally there is a need for such air-venting devices that vent gas bubbles in many medical, analytical, diagnostic and industrial applications, such as hot water heating systems, cardiopulmonary pumps, contrast solution power injectors, endoscopes, chromatography apparatuses, and microfluidic devices e.g., the Fluidigm devices such as those described in U.S. Pat. No. 7,118,910 “Microfluidic Device And Methods Of Using Same”; U.S. Pat. No. 6,752,922 “Microfluidic Chromatography”; and U.S. Pat. No. 6,951,632 “Microfluidic Devices For Introducing And Dispensing Fluids From Microfluidic Systems”; each of which is hereby fully incorporated by reference for all purposes to the extent allowed by law.
A number of references describe technology and devices relevant to the present invention and show some previous solutions to the present technological problems. But none of these references disclose or suggest the present invention. These references include the following.
U.S. Pat. No. 4,689,047 “Air Venting Winged Catheter Unit”. This disclosure describes a winged catheter unit enabling the user to introduce intravenous fluids while permitting the technician to control air venting at the onset of the I.V. introduction and during change of I.V. bottles without removal of the catheter.
U.S. Pat. No. 4,227,527 “Sterile Air Vent” describes a sterile air vent which permits the passage of gas but is substantially impervious to microorganisms. The vent is suitable as a tip protector for the tip ends of medical fluid administration sets or the like and filtering is provided by a solid micro-porous plug.
U.S. Pat. No. 5,334,153 “Catheter Purge Apparatus and Method of Use” describes balloon catheters with an air purging feature.
U.S. Pat. No. 4,324,239 “Safety Valve for Preventing Air Embolism and Hemorrhage” describes a safety valve with an integrated piston.
U.S. Pat. No. 5,533,512 “Method and Apparatus for Detection of Venous Air Emboli” describes a respiratory gas monitoring system to detect emboli.
U.S. Pat. No. 3,982,534 “Intravenous Administration System” describes an intravenous administration system with three separate units for delivering fluids.
U.S. Pat. No. 5,108,367 “Pressure Responsive Multiple Input Infusion System” describes an infusion system for administering multiple fluids at individually programmable rates and volumes. The system has a priming mode that detects and removes air bubbles in the fluid line.
U.S. Pat. No. 3,844,283 “Apparatus for Aseptically Dispensing a Measured Volume of Liquid Apparatus” discloses a device for dispensing volumes of liquid with a conventional cut-off valve to eliminate the need for introducing contaminating environmental air.
US20020022848A1 “Method and Apparatus for Minimizing the Risk of Air Embolism when Performing a Procedure in a Patient's Thoracic Cavity” describes an apparatus for minimizing the risk of air embolism includes an instrument delivery device having a gas outlet for delivering gas into a patient's thoracic cavity.
The present invention provides a simple and effective solution to the long-standing and well-known problem of gas bubbles in fluid-carrying lines. This problem is of considerable importance in various many applications, particularly in medical applications.